This invention relates to composite abrasive compacts.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. Abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline hard conglomerate. The abrasive particle content of abrasive compacts is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are generally made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable.
Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate or support. Such supported abrasive compacts are known in the art as composite abrasive compacts. The composite abrasive compact may be used as such in the working surface of an abrasive tool.
Examples of composite abrasive compacts can be found described in U.S. Pat. Nos. 3,745,623, 3,767,371 and 3,743,489.
Composite abrasive compacts are generally produced by placing the components, in particulate form, necessary to form an abrasive compact on a cemented carbide substrate. This unbonded assembly is placed in a reaction capsule which is then placed in the reaction zone of a conventional high pressure/high temperature apparatus. The contents of the reaction capsule are subjected to suitable conditions of elevated temperature and pressure.
It does happen from time to time that substantial portions of a composite diamond abrasive compact break off during use. The break off occurs through both the compact layer and the carbide substrate rendering that composite abrasive compact useless for further work. It is believed that this type of catastrophic failure results, in part, from stresses set up in the carbide substrate by an uneven distribution of binder metal in that substrate. During manufacture of the composite abrasive compact, binder from the substrate infiltrates the diamond layer resulting in binder-lean regions being formed in the carbide substrate. Such regions are susceptible to stress cracking.
U.S. Pat. No. 4,225,322 describes a method of fabricating a tool component comprised of a composite abrasive compact bonded to a carbide pin by a layer of brazing filler metal. The method involves placing a layer of the brazing filler metal between a surface of the carbide substrate of the composite abrasive compact and the pin and disposing the composite abrasive compact in thermal contact with a heat sink during the subsequent brazing operation. Bonding between the carbide substrate and the carbide pin takes place under ambient pressure conditions.